Elasticity

So the nerd in me is taking a class this semester called Physical Sciences 2: Mechanics, Elasticity, Fluids, and Diffusion (also known as PS 2), or basically the first semester of a year of physics!

Anyways, today's lecture was on elasticity. I can summarize ninety minutes of lecture (beginning at 9:30am ... which is quite early on my schedule) and a notebook of equations for you by saying that all solids essentially obey Hooke's law for small deformations. If we deform a solid slightly, this will lead to a linear restoring force, which is equivalent to that derived from simple harmonic oscillation, aka a spring!

So basically, at a very fundamental and slightly perturbed level, everything acts like a spring.

Thus, all solids have some sort of elasticity! Coming back to Hooke's law, we can generalize it by using stress, strain, and something called Young's modulus. Young's modulus is like a spring constant, but it depends only on the material and NOT the size or shape.

So the reason why I thought I'd bring this up is because the professor discussed the Young's modulus some examples of various biological and technological materials.

Teeth (dentine) has a Young's modulus of 1.5 x 10^10 Pascals.

That probably means nothing to you.

So for reference, bone has a slightly higher Young's modulus of 1.7 x 10^10 Pascals,  and steel has a Young's modulus of 2 x 10^11 Pascals.

Collagen (tendon) has a Young's modulus of 2 x 10^9 Pascals, and Elastin (skin) has a Young's modulus of 4 x 10^5 Pascals.

Take home message: if we were to make a spring composed of your (or my) teeth, it would be more springy than a spring made of your hip bone or your SUV, but less springy than one made of your skin.

Intuitive? Somewhat!
Biological? YES!

Eric